This invention relates generally to pressure transmitters. More particularly, the present invention relates to a pressure transmitter for use in clean environments.
Certain industrial processes require relatively clean processing environments compared to general manufacturing processes. Examples of such clean processes include semiconductor manufacturing, pharmaceutical manufacturing, and food processing. In such environments, it becomes very important to ensure that all processing equipment can perform its required function without contaminating the process.
One device that has become highly useful in industrial processing environments is the pressure transmitter. A pressure transmitter is a device that senses fluid pressure within a process and provides an electrical signal indicative of the pressure to a control system. Generally, pressure transmitters have a pressure sensor that includes a deflectable diaphragm that deflects in direct response to pressure applied thereto, and which has an electrical structure on the diaphragm that varies its electrical characteristic in response to diaphragm deflection and thus pressure. Pressure transmitters that use a capacitive pressure sensor, are generally filled with a dielectric fill fluid that increases the capacitance of the pressure sensor to increase sensor resolution. However, in the event that such a sensor were to develop a leak, the dielectric fill fluid, which is occasionally silicone oil, would spill into the system thus contaminating the product. Therefore, industrial processes which require very clean environments generally do not tolerate pressure sensors that use a fill fluid. Thus, pressure transmitters designed for such clean environments are generally required to sense process fluid pressure without the benefit of a fill fluid.
Although a number of pressure transmitters are known for clean environments, there is an ongoing need to provide simply and cost effective pressure transmitters for use in clean environments.
A pressure transmitter for clean processing environments is disclosed. The pressure transmitter includes a process connector, a weld ring, a pressure sensor module, a frame, and a housing. The process connector is coupleable to a source of process fluid and directs process fluid to the pressure sensor module. The process connector is sealed to the pressure sensor module to couple process fluid to the pressure sensor. A weld ring is disposed about the pressure sensor module and provides a secondary process fluid seal. The pressure sensor module is electrically coupled to measurement circuitry to provide digital data indicative of process fluid pressure. The frame is coupled to the weld ring and the housing is coupleable to the frame and weld ring such that the housing rests upon the weld ring when secured in place.
The pressure sensor module includes an isolator diaphragm that is operably coupled to a pressure sensor. The pressure sensor can include a deflectable silicon diaphragm having elements thereon that provide an electrical characteristic that varies with diaphragm deflection. The isolating diaphragm and deflectable diaphragm are separated from one another by a filler material. The filler material can be a polyurethane.